1. Field of the Invention
The present invention relates to a method and apparatus for measuring the surface shape of a thin element, i.e., a flat, board-like element, such as a silicon wafer by which the surface shape of the thin element measured with accuracy, and a method for measuring the thickness of such thin element. Thus, as used herein the term xe2x80x9cthin elementxe2x80x9d means such a thin flat, board-like member or element, for a specific purpose, without connoting or requiring that it be rectangular.
2. Related Art
Conventionally known apparatuses for measuring the surface shape of a thin element such as a silicon wafer are disclosed in, for example, Japanese Patent Publication No. Hei 5-77179, Japanese Patent Laid-Open Publication No. Hei 10-47949 and others.
FIG. 15 shows the apparatus disclosed in Japanese Patent Publication No. Hei 5-77179. This apparatus has a thin element 2 such as a silicon wafer adsorbed and supported by a rotatable vacuum chuck 1. A displacement meter 3 is disposed on either side of thin element 2 and supported by arm 4 and supporting member 5.
To evaluate the shape of thin element 2 by the apparatus, deviation in a group of thickness data obtained by measuring in a necessary region is determined to be the flatness of the thin element 2 because the thin element 2 is assumed to be used in a state tightly adhered to a reference plane such as a flat surface.
Such conventional evaluation method had a disadvantage that the surface of thin element 2 tightly adhered to the reference plane had local irregularities, or even if its thickness was uniform, waviness with a small cycle. When the surface was not fully adhered to the reference plane, such irregularity or waviness also was indicated as a shape formed on the opposed surface, and an overestimate or an underestimate might be made in evaluating the shape of the silicon wafer or the like to which a fine pattern was drawn or transferred.
For example, FIG. 16(a) shows that when local recess 2b having a length of a few millimeters to a few tens of millimeters is formed on back surface 2a of thin element 2 made of silicon wafer, thin element 2 cannot be tightly adhered with certainty to reference plane K by a suction force of a vacuum adsorption disk when a pattern is transferred; the evaluated result of flatness based on data of thickness shows that recess 2b is present on front surface 2c of thin element 2 as shown in FIG. 16 (axe2x80x2), and it is judged that thin element 2 is defective even if it has a shape good enough to transfer the pattern.
Also, for example, when local projection 2d having a length of a few millimeters to a few tens of millimeters is formed on back surface 2a of thin element 2 as shown in FIG. 16(b), the periphery of the projection 2d cannot be tightly adhered to reference plane K; the evaluated result of flatness based on data of thickness shows that projection 2d smaller than the actual one is present on front surface 2c of thin element 2 as shown in FIG. 16(bxe2x80x2), and the pattern is defectively transferred in a region broader than the one actually evaluated.
Moreover, when thin element 2 has a uniform thickness and waviness with a short cycle as shown in FIG. 16(c), back surface 2a of projection 2e cannot be tightly adhered with certainty to reference plane K; the evaluated result of flatness based on data of thickness shows that thin element 2 has a flat state as shown in FIG. 16(cxe2x80x2), resulting in the causation of a defective transferring of a pattern which cannot be presumed from the evaluation.
Since the conventional apparatus aims to measure the thickness of thin element 2, a constant relative distance between pair of displacement meters 3 for measuring both surfaces of thin element 2 has to be maintained. As shown in FIG. 17, forked holding part 6 is disposed to have thin element 2 therebetween; displacement meters 3 are mounted at the leading ends of holding part 6; and root part 7 of holding part 6 is supported to move holding part 6. Therefore, the conventional apparatus had the following disadvantages.
Specifically, when thin element 2 has a diameter as large as 300 mm, forked holding part 6 is required to have the length of at least 150 mm to measure the entire surface of thin element 2, and its root part 7 is also 150 mm or more millimeters away from displacement meters 3. Therefore, the moving accuracy of root part 7 is enlarged, an error is caused due to straightness of displacement meters 3, and an Abbe error is caused because the measurement points of pair of displacement meters 3 are deviated.
Also, when forked holding part 6 vibrates like a tuning fork, the relative distance between the pair of displacement meters 3 is varied, resulting in causation of an error.
The present invention was achieved in order to remedy the existing problems described above. It is an object of the invention to provide a method and apparatus for measuring the surface shape of a thin element with high accuracy the surface shape of a thin element such as a silicon wafer, glass for liquid crystals or a masking member.
Another object of the invention is to provide an apparatus with a simple structure for measuring surface shapes of thin elements, and which particularly can measure the surface shape of a thin element with high accuracy.
Another object of the invention is to provide a method for measuring the thickness of a thin element, with high accuracy as required.
A method for measuring the surface shape of a thin element according to the present invention comprises supporting the thin element so to be rotatable within a single plane, disposing first and second guide shafts respectively on one side and the other side of the plane so as to be parallel to the plane and to each other, measuring the distance each to one surface and to the other surface of the thin element by the first and second measuring means which independently moves along the first and second guide shafts, and measuring the surface shapes of one surface and the other surface of the thin element.
Another method for measuring the surface shape of a thin element according to the present invention comprises supporting the thin element so as to be movable within a single plane, disposing first and second guide shafts respectively on one side and the other side of the plane so as to be parallel to the plane and to each other, measuring the distance each to one surface and to the other surface of the thin element by the first and second measuring means which independently moves along the first and second guide shafts, and measuring the surface shapes of one surface and the other surface of the thin element.
An apparatus for measuring the surface shape of a thin element according to the present invention comprises a supporting means for supporting the thin element so to be rotatable within a single plane, first and second guide shafts which are disposed respectively on one side and the other side of the said plane so to be parallel to the plane and to each other, first and second sliders which move independently along the first and second guide shafts, and first and second measuring means which are fixed to the first and second sliders and which independently measure the distance each to one surface and to the other surface of the thin element.
Another apparatus for measuring the surface shape of a thin element according to the present invention comprises a supporting means for supporting the thin element so to be movable within a single plane, first and second guide shafts which are disposed respectively on one side and the other side of the said plane so as to be parallel to the plane and each other, first and second sliders which move independently along the first and second guide shafts, and first and second measuring means which are fixed to the first and second sliders and which independently measure each distance to one surface and the other surface of the thin element.
The apparatus for measuring the surface shape of a thin element according to the present invention further comprises aligning means for positioning the first and second measuring means on the same axial line which is perpendicular to the plane.
A method for measuring the thickness of a thin element according to the present invention measures the thickness of each part of the thin element based on the surface shapes of one surface and the other surface of the thin element as measured by any of said methods for measuring the surface shape of a thin element according to the invention and the distance between the first and second measuring means.